1. Field of the Invention
The present invention relates to a moving-picture encipherment method and system, and an enciphered moving-picture decipherment method and system. The moving-picture data processed consists of intra-frame encoded moving-picture data frames and inter-frame encoded moving-picture data frames. In detail, the present invention relates to the encipherment method and system by which highly safe encipherment of the moving-picture data can be easily achieved, and to the decipherment method and system by which the moving picture enciphered through the encipherment method can be easily deciphered.
Distribution of moving-picture data has been proposed such that moving-picture data which is recorded in a recording medium such as a CD-ROM or the like as a file is provided to a user, or moving-picture data is directly transmitted to a terminal unit of a user via a communication network. In such moving-picture data distribution, it is necessary to protect the copyright of the moving-picture data and to charge for distributing it. Therefore, it is necessary to prevent moving-pictures from unauthorized use. For this purpose, moving-picture data is enciphered.
2. Description of Related Art
In the field of broadcasting and so forth, relatively simple encipherment is performed such as scan lines being replaced. Application of such a moving-picture data enciphering method used in the broadcasting field and so forth to encipher moving-picture data handled by a computer will now be considered. If such an application is provided, moving-picture data enciphering can be relatively easily performed but deciphering of the enciphered data can also be performed relatively easily. Thus, a problem is presented as to the safety of the enciphered data.
It is possible to use a high-order encipherment algorithm such as a highly safe DES (Data Encryption Standard) or the like. However, a moving picture has a very large amount of data. Therefore, if all moving-picture data representing a moving picture is enciphered in accordance with such a highly safe encipherment algorithm, it may be difficult to perform an enciphering operation within an appropriate time.